Hey, i am relatively new here (still less than a month) and you are right, there is a wealth of knowledge here and most people are happy to share (if you have used the search function first haha). Sometimes using that though brings up as many questions as it answers, so i'll try to help you out with what i know so far.
1) Test size: settings>screen>text size. There is a keyboard that you can download that makes so when you push a button, instead of just enlarging the keyboard it displays the pressed key above where your finger is so i you can actually see it. Unfortunately i just came across it earlier today in the forums and can't remember where, if i find it i'll post the link. Other than that i am not really sure if any others than the one you've mentioned.
2) Sorry, i can't really help here
3) I really only know about PIM backup, however i don't know if it has cross-device functionality. If they have a PALM version you could give it a go, it just creates a file that you can restore contacts etc. from. Other than that i can only think of doing it via syncing PALM with computer, and then doing it with the Diamond (is this what you were referring to when contact sync failed?)
4)Some programs rotate automatically such as the picture viewer and opera, but the 3rd party program requires you to press and hold the send key. I don't know which you are referring to.
5) settings>remove programs
6) "Clear storage" is essentially the same as a hard reset. It erases EVERYTHING that you have added from the MAIN storage (not the internal 4gb, it leaves this intact) and replaces it with everything default. "Format Internal Storage" erases EVERYTHING from the 4gb internal storage. Finally, "Clear storage and format internal storage" does both of these, erasing anything you've added to the phone and putting it back to the stock ROM settings. This means it will be the same as the day you bought it you haven't replaced the rom, or will be he default as set by the cooked rom (ex. Juicy ROM or MightyStable ROM)
7) Those boxes that you are checking for the home screen are for the Windows home screen, not TF3D, which is the program with all the tabs. If you uncheck TF3D from that same section, it will turn it off and replace it with a very simple Windows home screen with all the other options who have checked.
Choose open if you just want to run whatever the file is, save if you want to keep the file for future use (either works, it is just a matter of do you want it to take up space). Most people advise to install to the internal memory, because that is the 4gbs, but yes, some programs need to be installed to the Device although it will usually tell you when this is the case.
I know i wasn't able to answer everything, but i hope some of that was able to help you.